Depth image plays an important role in various applications such as robotics, human-machine interaction, augmented reality and the like. Particularly, consumer-grade depth sensors make various depth-based applications possible. These applications include, for example, controller-free video games, simple 3D-reconstructions and the like.
Since the quality of depth image influences the performance of a depth-based application, researchers have developed and extended various image filters for depth image restoration and enhancement. These methods may be generally classified into methods based on filtering and methods based on optimization. Generally, the methods based on filtering are faster but have limited enhancement performance, while the methods based on optimization are slower but have good enhancement capabilities.